Lymph nodes characterization plays an important role in cancer staging and detecting local or distant recurrences. Previous studies have demonstrated the usefulness of ultrasound backscatter coefficients (BSCs) at high frequencies (16.4 - 33.6 MHz) for detecting micro-metastasis of colorectal, gastric and breast cancers in lymph nodes. However, these studies were conducted ex vivo. In this work, the feasibility of diagnosing metastatic cervical lymph nodes in vivo using BSCs within a clinical frequency range (3.5 - 10 MHz) was evaluated. The reference phantom method was used to estimate the BSC curves from 24 patients examined in a local oncology center for suspicious cervical nodes (metastatic spread at diagnosis or tumor recurrence). For all cases, the diagnosis was provided by a trained histopathologist through confirmatory biopsies. Classification was performed using linear logistic regression with leave-one-out cross-validation and operating points chosen to maximize Youden's index in the corresponding ROC curves. Overall, 12 out of 24 cases had malignant infiltration (50%). The BSC slope and intercept values for the malignant cases were higher and lower than the ones of the benign cases, respectively. Classification using both parameters resulted in a sensitivity of 91.7% and a specificity of 75%. This study presents the first report of in vivo assessment of lymph nodes for metastatic infiltration using BSCs. The preliminary results suggest that it may be possible to discriminate between benign and malignant nodes using BSCs in vivo.